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Cream
Cream is one of several dilution loci which lighten the colour of a horse's base coat. The various cream alleles determine whether cream dilution occurs and to what extent. When creating a custom horse (or using the custom previewer), the user is asked to select the specific genotype at the cream locus, rather than choosing a phenotype and having the game select an appropriate genotype. There is no correlation between island of origin and cream allele frequency, although some alleles are rarer than others. Alleles There are three cream alleles, though their interactions when it comes to determining phenotype are far from simple. n The n allele represents an inactive cream allele, and does not exert any dilution upon a horse's base coat. It is co-dominant with respect to Cr and dominant with respect to prl. When the cream locus is homozygous for n, it is not displayed in the Genetics field of a horse's page. It can be obtained using a Drop Gene item and selecting 'Cream' or 'Pearl' as appropriate. Cr The Cr allele is able to exert strong dilution on a horse's coat. It is co-dominant with respect to n and prl. It can be obtained using the Add A Gene: Cr item. It is inactive in donkeys. prl The prl allele is much rarer than the other two cream alleles and exerts a weaker affect than Cr. Interestingly it behaves differently in Arabians and mules than in horses of other builds and is inactive in donkeys. It is recessive with respect to n but co-dominant with respect to Cr. It can be obtained using the Add A Gene: prl item. Phenotypes Non-Cream (nn, nprl) A non-cream horse is not experiencing dilution due to the cream locus (though other dilution loci may be in affect). Donkeys always display this phenotype, regardless of their genetics at the cream locus, while mules with one or more prl copies will also display this phenotype. Cream (nCr) A cream horse experiences strong dilution of its base coat. In black-based horses the lower legs, muzzle, mane and tail are not affected, but all areas of a red-based horse are, indeed the mane and tail seem to be diluted more strongly than the body in such a horse. The cream phenotype may be designated by another term in the horse's colour description, for example a bay cream horse is termed a buckskin and a chestnut cream horse is termed a palomino. As the Cr allele is inactive in donkeys, they never display this phenotype. Homozygous Cream (CrCr) A homozygous cream horse is diluted even more strongly than a cream horse, which, depending on the extension and agouti phenotypes, may result in the horse being off-white in colour. Interestingly, prlprl Arabian horses are identical to homozygous cream horses. The homozygous cream phenotype is never referred to as such in a horse's colour description, instead other terms are used. For example, a bay homozygous cream is called a perlino and a chestnut homozygous cream horse is termed a cremello. As the Cr allele is inactive in donkeys, they never display this phenotype. Faux homozygous cream (Crprl) A faux homozygous cream horse looks essentially identical to a homozygous cream horse. In a horse's colour description, faux homozygous cream is simply marked by the word 'faux' before the homozygous cream term, for example 'faux perlino'. As the Cr and prl alleles are inactive in donkeys, they never display this phenotype, while in mules, the prl allele appears to counteract, rather than exacerbate the effect of the Cr allele, and Crprl donkeys have the non cream donkeys. Pearl (prlprl) A pearl draft, warmblood, pony or Arabian of evolution level 2 or higher exhibits milder dilution than a cream horse, though the dilution is more even, with less difference between the dilution effect on the body and the extremities (e.g. tail, lower legs). A prlprl Arabian of less than level 2 evolution is visually indistinguishable from a homozygous cream, and is termed as such in the horse's colour description. Meanwhile, a prlprl mule has a non-cream phenotype. Otherwise, the pearl phenotype is marked simply by the addition of the word 'pearl' to the base coat descriptor, or is combined with the extension and agouti allele markers, for example, a chestnut pearl is termed an apricot. Category:Base Coat Genetics